1. Field of the Invention
The present invention relates to a method for producing a Group III nitride semiconductor product whose main surface is a non-polar plane (e.g., m-plane or a-plane) or a semi-polar plane (e.g., r-plane). The present invention also relates to a template substrate including a growth substrate and a Group III nitride semiconductor whose main surface is a non-polar plane or a semi-polar plane, the Group III nitride semiconductor being formed on the growth substrate.
2. Background Art
Hitherto, Group III nitride semiconductor device have been produced by stacking a Group III nitride semiconductor on a growth substrate (e.g., a sapphire substrate) in a c-axis direction. However, due to strain in the crystal structure of the Group III nitride semiconductor, a piezoelectric field is generated in a c-axis direction of the semiconductor, which may cause deterioration of device performance. When, for example, a light-emitting device is produced through the aforementioned process, internal quantum efficiency is lowered.
In recent years, in order to avoid deterioration of device performance due to generation of a piezoelectric field, attempts have been made to develop techniques for crystal growth of a Group III nitride semiconductor whose main surface is a non-polar plane (e.g., a-plane or m-plane) or a semi-polar plane (e.g., r-plane). Also, attempts have been made to use, as a growth substrate, a GaN substrate or GaN template substrate whose main surface is a non-polar plane (e.g., a-plane or m-plane) or a semi-polar plane (e.g., r-plane).
In a known crystal growth technique, a GaN substrate having an m-plane or a-plane main surface is used as a growth substrate. Such an m-plane or a-plane GaN substrate is produced by growing a thick GaN layer having a c-plane main surface on a growth substrate (e.g., sapphire) and cutting out the thus-grown GaN layer parallel to m-plane or a-plane.
Japanese Patent Application Laid-Open (kokai) No. 2006-36561 discloses production of GaN crystal or GaN template substrate having an a-plane or m-plane main surface, through the following process: stripe-pattern grooves are formed in a sapphire substrate (i.e., growth substrate) having an a-plane or m-plane main surface so that the longitudinal direction of the grooves is a c-axis direction; an SiO2 mask is formed on the surface of the growth substrate, one side surface of each groove, and a portion of the bottom surface of the groove; a buffer layer is formed only on the other side surface of the groove; and GaN is grown on the side surfaces of the grooves on which the buffer layer has been formed.
However, when an m-plane or a-plane GaN substrate is produced through a conventional method, the size of the substrate cannot be increased, since the substrate size depends on the thickness of a GaN layer. In addition, the conventional method fails to mass-produce such a GaN substrate. When a GaN layer is formed on a growth substrate, a portion of the GaN layer proximal to the substrate exhibits poor crystallinity, whereas a portion thereof distal to the substrate exhibits good crystallinity. Therefore, in-plane variation in crystallinity occurs in an m-plane or a-plane GaN substrate produced through cutting out of the GaN layer.
The method disclosed in Japanese Patent Application Laid-Open (kokai) No. 2006-36561 encounters difficulty in selectively forming a mask or a buffer layer, and in growing, with high reproducibility, a Group III nitride semiconductor exhibiting good crystallinity and having an a-plane or m-plane main surface.